Найдите значение выражения 1/5⋅12+1/12⋅19+…+1/698⋅705

\dfrac{1}{5\cdot 12}+\dfrac{1}{12\cdot 19}+\dfrac{1}{19\cdot 26}+...+\dfrac{1}{691\cdot 698}+\dfrac{1}{698\cdot 705}=\\ \\ =\dfrac{1}{7}\cdot \left(\dfrac{12-5}{5\cdot 12}+\dfrac{19-12}{12\cdot 19}+\dfrac{26-19}{19\cdot 26}+...+\dfrac{698-691}{691\cdot 698}+\dfrac{705-698}{698\cdot 705}\right)=

=\dfrac{1}{7}\cdot \left(\dfrac{1}{5}-\dfrac{1}{12}+\dfrac{1}{12}-\dfrac{1}{19}+\dfrac{1}{19}-\dfrac{1}{26}+...+\dfrac{1}{691}-\dfrac{1}{698}+\dfrac{1}{698}-\dfrac{1}{705}\right)=\\ \\ =\dfrac{1}{7}\cdot \left(\dfrac{1}{5}-\dfrac{1}{705}\right)=\dfrac{1}{7}\cdot \dfrac{4}{21}=\dfrac{4}{147}